1. Field of the Invention
The present invention relates to a hybrid drive power apparatus for a motor vehicle, particularly to an improvement for decreasing loss of drive power caused in a power transmission of the dual-clutch type suitable for applied to a hybrid drive power apparatus.
2. Discussion of the Prior Art
Disclosed in Japanese Patent Laid-open Publication No. 2005-186931 is a hybrid drive power apparatus provided with a power transmission of this type. The hybrid drive power apparatus includes first and second input shafts arranged to be selectively rotated by drive power of an engine transmitted thereto through a dual-clutch, first and second gear-shift mechanisms respectively assembled with first and second output shafts in parallel with the first and second input shafts, and a motor-generator in drive connection with the second output shaft to be activated as an electric motor for driving a set of driven road wheels through a final output shaft in drive connection with the first or second output shaft when supplied with electric power from a battery and to be activated as a generator for charging the battery when driven by the driven road wheels.
3. Problems to be Solved
In the hybrid drive power apparatus, the first and second friction clutches are alternately engaged to selectively transfer drive power of the engine to the first or second input shaft so that the drive power is transferred to the final output shaft in drive connection to the drive road wheels at a shift step selected in the first or second gear-shift mechanism. When the motor-generator in drive connection with the second input shaft is activated as an electric motor, drive power of the motor-generator is transferred to the final output shaft through the second input shaft and the second gear-shift mechanism. Assuming that the motor-generator is activated as the electric motor in a condition where the first friction clutch has been brought into engagement to transfer the drive power of the engine to the final output shaft through the first gear-shift mechanism, the drive power of the motor-generator is transferred to the final output shaft through the second input shaft and the second gear-shift mechanism. In such an instance, the second friction clutch is released for disengagement during which the input and output members of the second friction clutch are forced to relatively rotate since a change-speed ratio between the output shaft of the first gear-shift mechanism and the input member of the first friction clutch is different from a change-speed ratio between the output shaft of the second gear-shift mechanism and the input member of the second friction clutch. Even when the second friction clutch is in a released condition, drag torque is caused by friction resistance between the input and output members of the second friction clutch. The occurrence of such drag torque causes loss of the drive power. In the case that a wet-type friction clutch is used as the second friction clutch, the drag torque becomes large, resulting in increase of loss of the drive power.